The present invention relates to a process and a device for guiding a flying craft, in particular a missile, onto a target.
More precisely, the said process and device are intended for implementing autoguidance, that is to say guidance which can be carried out solely with the aid of the information available on the said flying craft.
In a known manner, for a missile, in particular an air-to-ground missile, such autoguidance is implemented in the terminal phase of the guidance, on approach to the target.
Generally, the said autoguidance is carried out with the aid of information supplied by a seeker head, and in particular of the information relating to the said target which is situated in a field of view of the said seeker head. To this end, the line of sight of the seeker head is continually servocontrolled.
In a known manner, such servocontrol exhibits different objects, depending on the guidance phase considered, and consisting:
before xe2x80x9clock-onxe2x80x9d, that is to say before actual detection of the target, in pointing the said seeker head within the assumed environment of the said target; and
after xe2x80x9clock-onxe2x80x9d, in maintaining the target within the measurement field (restricted by design) of the said seeker head and in tracking the said target.
The guidance commands for the said flying craft are then deduced, in a known manner, by using the signals supplied by the seeker head tracking the target, the said guidance commands being implemented by the steering of the craft carrying out the commanded maneuvers in terms of pitch and yaw, possibly with roll servocontrol, either to keep the roll of the craft constant, or to distribute the aerodynamic load by performing an aerodynamic roll check of the craft so as to improve the aerodynamic characteristics such as the useable load factor, the load on the steering actuators, the roll torques induced, etc.
This standard solution of autoguidance nevertheless has a number of drawbacks. In particular, it is complex and expensive, since it requires, in a known manner, for its implementation, in addition to the seeker head detection system, several other expensive measurement and processing devices, in particular:
mechanical devices for rendering the line of sight moveable, with mobility according to at least two or three axes for guidance in space. These mechanical devices comprise, for example, articulations with a gimbal mounting and motorization of each axis;
measuring equipment and associated electronic means for monitoring line of sight servocontrol loops.
To remedy these drawbacks, it is known practice to use a detector, for example of the infrared or optical detection type, in particular laser detection, which is rigidly tied to the flying craft and which carries out the overall function of detection (location and identification) of the target.
However, such an implementation, which exhibits undeniable advantages relative to the aforesaid standard solution, requires a detector exhibiting a measurement field of considerable size so as, the flying craft being guided on a trajectory toward the target:
before lock-on, to have the target in the said measurement field, whilst taking into account, not only errors in objective designation and guidance of the craft, but also incidences of the said craft due to the disturbances of the environment (wind, effect of gravity, etc.) and to the achieving of the load factor; and
after lock-on, continuing to maintain the target in the said measurement field.
Of course, the requirement of a considerable size for the field of measurement of the detector entails drawbacks, in particular in terms of cost, bulk, weight, etc.
The object of the present invention is to remedy these drawbacks and in particular to reduce the size of the field of measurement of the detector whilst remaining compatible with the effectiveness of guidance. It relates to a process for guiding a flying craft onto a target, the said guiding exhibiting various successive phases, including a terminal phase for which at least the guidance is carried out with the aid of measurements performed by a detector mounted on the said flying craft and pointed with its line of sight toward the said target so that a projection of the latter is situated on a field of measurement of the said detector, as well as with the aid of information, in particular navigation and inertial information, emanating from information sources mounted on the said flying craft.
To this end, according to the invention, the said process is noteworthy in that at least in the said terminal phase, attitudes of the said flying craft are controlled in such a way as to center the projection of the target with respect to a first direction of the said measurement field, in that the line of sight of the said detector is moveable about a second direction of the said field of measurement, which is different from the said first direction, and in that at least in the said terminal phase, the mobility of the line of sight of the said detector is controlled in such a way as to center the said projection of the target with respect to the said second direction.
Thus, since by virtue of the invention the projection of the target onto the field of measurement of the detector is automatically centered with respect to the said first and second directions which are orthogonal, respectively by controlling the attitudes of the flying craft and the mobility of the said line of sight, the said measurement field may exhibit a reduced size so that the said detector makes it possible to remedy the aforesaid drawbacks (cost, bulk, weight, etc.).
Advantageously, at least in the said terminal phase, the relative motion between the flying craft and the target is estimated, thus making it possible in particular to estimate the kinematics of the target with respect to the flying craft and thus to implement the process in accordance with the invention even:
when the projection of the target leaves the field of measurement of the detector; and even
in flight phases for which such a projection does not exist or does not yet exist.
Moreover, advantageously, at least in the said terminal phase, attitudes of the said flying craft are controlled in such a way as to distribute the aerodynamic load over axes tied to the said flying craft.
Such a distributing of the aerodynamic load exhibits several advantages and makes it possible in particular:
to relieve the actuators of the steering control surfaces of the flying craft; and
to increase the total steerable domain of incidence.
Moreover, advantageously, the roll of the flying craft is controlled as attitude of the latter.
Thus, since the guidance of the flying craft is carried out in a standard manner in terms of pitch and yaw, the (roll) control in accordance with the invention with a view to the centering and, as appropriate, the distributing of the aerodynamic load is compatible with the effectiveness of the guidance.
To determine a roll control command, use is preferably made for this purpose of the deviation measurement values determined at least from certain of the following information:
information relating to measurements performed by the said detector;
inertial information and navigational information; and
information relating to the orientation of the line of sight of the detector, with respect to the flying craft.
In an advantageous mode of implementation, to simultaneously carry out a distributing of the aerodynamic load over axes tied to the flying craft and the centering of the projection of the target, the roll is controlled on the basis of a roll variation command xcex94xcfx86co which satisfies the relation:       Δ    ⁢          xe2x80x83        ⁢    ϕ    ⁢          xe2x80x83        ⁢    co    =      {                                                      ΔΔϕ              ⁢                              xe2x80x83                            ⁢              coA                        ,                          if              ⁢                              xe2x80x83                            ⁢              the              ⁢                              xe2x80x83                            ⁢              value              ⁢                              xe2x80x83                            ⁢              Δϕ              ⁢                              xe2x80x83                            ⁢              coA              ⁢                              xe2x80x83                            ⁢              is              ⁢                              xe2x80x83                            ⁢              defined              ⁢                              xe2x80x83                            ⁢              between                                                                                                      values                ⁢                                  xe2x80x83                                ⁢                Δϕ                ⁢                                  xe2x80x83                                ⁢                co1                ⁢                                  xe2x80x83                                ⁢                and                ⁢                                  xe2x80x83                                ⁢                Δϕ                ⁢                                  xe2x80x83                                ⁢                                  co2                  ·                  Δϕ                                ⁢                                  xe2x80x83                                ⁢                coE                            ,              otherwise                        ⁢                          xe2x80x83                                          
in which:
xcex94xcfx86coA is a standard roll variation command for distributing the aerodynamic load;
xcex94xcfx86co1 and xcex94xcfx86co2 are roll variation commands determined from the actual state of the said flying craft; and
xcex94xcfx86coE is a roll variation command determined from the said commands xcex94xcfx86co1 and xcex94xcfx86co2.
Moreover, advantageously, the said roll variation commands xcex94xcfx86co1 and xcex94xcfx86co2 respectively satisfy the following relations:             tan      ⁢              xe2x80x83            ⁢      Δϕ      ⁢              xe2x80x83            ⁢      co1        =                  U1        +        UO1                              [                                                    "LeftBracketingBar"                U2                "RightBracketingBar"                            e                        +            K                    ]                xc3x97                  Sign          ⁡                      (            U2            )                                          tan      ⁢              xe2x80x83            ⁢      Δϕ      ⁢              xe2x80x83            ⁢      co2        =                  U1        -        UO2                              [                                                    "LeftBracketingBar"                U2                "RightBracketingBar"                            e                        +            K                    ]                xc3x97                  Sign          ⁡                      (            U2            )                              
in which:
tan represents the tangent;
e, K, U01 and U02 are predetermined values; and
U1 and U2 are deviation measurement values.
In order to increase the performance of the processing implemented, advantageously, the said deviation measurement values U1 and U2 respectively satisfy the following relations:
U1=xcex8+EBZu
U2=xcex8+EBYu
in which xcex8+EBZu and xcex8+EBYu respectively represent deviations in pitch and yaw attitudes with respect to the craft/target straight line which are determined, on the one hand from pitch and yaw attitudes prescribed by the guidance of the flying craft and, on the other hand, from current pitch and yaw attitudes of the flying craft.
Furthermore, advantageously, the controlled deviations of attitudes with respect to the craft/target straight line are limited to predetermined values, thus making it possible in particular to limit the guidance of the flying craft with respect to the pointing of the target and hence to favor this pointing.
With this in mind, in a particular embodiment, commands for controlling variations in attitudes are determined in such a way as to favor, according to the flight phase considered, at least one of the following actions: the guidance of the flying craft, the centering of the projection of the target on the detector and the distributing of the aerodynamic load.
Additionally, the said flying craft can be guided in such a way as to limit its kinematic incidence and its kinematic sideslip, at least in an ultimate phase of the said terminal phase, that is to say preferably just before contact with the target, in particular so as to favor the effectiveness of the destruction of the latter.
The present invention also relates to a device for guiding a flying craft onto a target, the said device comprising:
information sources generating information relating to the said flying craft;
a detector capable of carrying out measurements relating to the target, and mounted on the said flying craft and pointed with its line of sight toward the said target so that a projection of the latter is situated on a field of measurement of the said detector;
a computation unit for determining, from the said information and the said measurements, at least in a terminal phase of the said guidance, guidance commands; and
steering members carrying out the guidance of the said flying craft as a function of the said guidance commands.
According to the invention, the said device is noteworthy in that it moreover comprises computation means for determining commands for varying attitudes of the said flying craft making it possible to center the projection of the said target with respect to a first direction of the said measurement field, the said attitude variation commands being transmitted to the said steering members, in that the said detector exhibits a line of sight which is moveable according to a second direction of the measurement field, which is different from the said first direction, in that the device in accordance with the invention comprises orientation means controllable so as to orient the said line of sight of the detector, and in that the said computation means control the said orientation means in such a way as to obtain the centering of the said projection of the target with respect- to the said second direction.
Thus, the device in accordance with the invention is uncomplicated and inexpensive.
Moreover, advantageously, the said device comprises:
a means for estimating the relative motion between the flying craft and the target. The estimations thus carried out may be used to increase the accuracy and performance of the device and also to offset the absence of the projection of the target in the measurement field; and/or
a means for supervising the said device, which is preferably formed in such a way as to favor, according to the flight phase considered, at least one of the following actions:
the centering of the projection of the target on the measurement field of the detector;
the guidance of the flying craft; and
the distributing of the aerodynamic load over axes tied to the said flying craft.
Furthermore, to simplify the embodiment advantageously, the said computation means are integrated into the said computation unit.
Additionally, advantageously, the mobility of the said line of sight corresponds to an orientation about an axis tied to the craft. The device according to the invention therefore requires few moveable parts, the mobility being implemented according to a single axis, and with motorization which may be crude, as stated hereinbelow, whilst retaining a reduced size of the measurement field.
Furthermore, in a preferred embodiment, the said orientation means comprise:
an optical relay system, comprising for example a fixed mirror, a moveable mirror and a focusing optic;
a motor, preferably a torque motor; and
a means of duplicating the orientation comprising, for example, a potentiometer.
The figures of the appended drawing will clearly elucidate the manner in which the invention may be embodied. In these figures, identical references denote similar elements.